Comments on: The Low Spark of Raised-Heel Trusses

By: Bill Hawkins

Bill Hawkins — Wed, 20 Feb 2019 20:38:03 +0000

I am following up on my
I am following up on my original posting. I did quite a bit of research about the best way to protect the fiberglass insulation that is often left exposed behind the soffits after making this posting. The recommended way to protect the fiberglass is to continue the sheathing (typically OSB) above the top of the wall to within 3 or 4″ of the underside of the roof sheathing. This detail directs any air flow over the top of the insulation and into the attic. It has the additional advantage that the trusses are tied to the walls with sheathing.
In my case, it would have been a lot of work to remove the soffits and then install additional OSB, etc.
I came up with a good way to accomplish the same goal. I made some 1/2″ exterior plywood panels that fit between adjacent trusses and between the top plate of the wall and the roof sheathing. I made these panels about 1/2″ narrower and 1/2″ shorter than the opening, so the plywood itself easily fit into the space. Then I stapled a folded double layer of double bubble around the perimeter of the plywood. The double bubble creates gasket that makes a good seal between the trusses, the top plate and the sheathing. I used a hole saw to cut 3 2 1/2″ holes in the plywood. These holes were in a row near the top of the panel. Then I solvent welded 3 1/3′ long pieces of 2″ PVC plumbing pipe (a 10′ length cut in 3 pieces) into the holes simply by cutting 1/2″ pieces of 2″ PVC tube and then slicing them so I could spread them to fit around the PVC on both sides of the plywood and solvent welding them to the tube. These ~3′ long pieces of PVC acted as a handle that allowed me to insert the plywood baffles between each set of trusses from the attic. It was pretty easy to do this while laying on a couple of 2 by 8 planks resting on the ceiling joists. I put a 2 by 2 between each set of trusses about 3′ above the energy heals and then used deck screws to fasten the other end of the PVC tubing just under the roof sheathing. I completed the windward side of the attic with about 2 days work. There is still a good amount of ventilation in the attic, and no risk of ice damming. 3 PVC tubes provide about 10 sq inches of ventilation. I was able to complete this work in the early winter because everything was done inside the attic. Thought I’d pass on this solution because it is pretty simple and the materials are all quite inexpensive and readily available.

By: Mark

Mark — Wed, 20 Feb 2019 18:30:53 +0000

In reply to Bill Hawkins. Bill,
Bill, I see no response to your post. I'm building a new home in Zone 7/8 intersection on a large lake with similar off water winds in the winter. I am contemplating building a home roof with no roof ventilation by not installing eve vents and using spray foam insulation under the roof deck which will help avoid the similar problem of snow moisture that you experienced. Downside is conditioning space in the attic that is not used except for possible installation of AC ducts in the attic. Problem with that is introducing moisture via leaking duct work in the attic but with closed cell foam hopefully that will not be a problem with rotting deck boards. I have also heard some discussion regarding a polystyrene foam board placed above the roof decking but it has been difficult to find information on that concept but it would have to be used in conjunction with spray foam under the deck board to get the minimum R-50. Would you have ever considered a non-ventilated roof system if your were building the home new today?

By: Nate Joseph

Nate Joseph — Thu, 24 May 2018 20:16:39 +0000

In reply to RoyC. In my opinion, the double top
In my opinion, the double top plate provides more Pros than Cons. In no particular order let me see if I can list the advantages. 1. The obvious one, it provides a solid, continuous bearing condition for Rafters, Trusses and Floor Framing so that theses members do not necessarily have to align with the vertical members below the double top plate. 2. It is a lot easier to achieve a continuous length. By staggering the splice locations you can have a continuous solid member unlike a single plate where you're forced to bundle studs below the splice point. 3. It provides the opportunity to tie perpendicular walls at the plates. The upper top plate can be notched to receive the upper top plate from a perpendicular wall, thus tying the two walls together at that point to provide additional strength. 4. It gives a larger nailing surface for attachment of structural clips, straps and hold-downs in addition to crown molding, trim, sheathing and drywall.

By: Bill Hawkins

Bill Hawkins — Mon, 20 Nov 2017 23:57:44 +0000

I had a new house built in
I had a new house built in 2008 with energy heel trusses. This house is built at the top of a steep ~130' cliff along a bend in a river gorge. This is a beautiful place with great views, but there are one or two times every winter when it snows and then there is a strong wind that blows snow into the attic because of the updraft caused by the cliff. Snow drifts next to the house are often 4 to 6' deep after these wind storms. (This spot is a place where eagles play in the strong updrafts when it is warmer out) Because of wind washing, some of the snow makes it under the insulation and there is some slight staining of the ceiling sheet rock. I have done quite a bit of building myself, and am looking for a design detail that will allow me to restrict air flow through the soffit vents on this side of the house. I'd like to do this from inside the attic. The roof pitch is 7/12 and the attic insulation is a single layer of kraft faced R38. One thing I am thinking of doing (after restricting air flow into the attic) is to add another layer of unfaced R19 insulation running perpendicular to the direction the trusses run. Please let me know if you have any recommendations about how to solve this problem.

By: Rob Kinsey

Rob Kinsey — Mon, 02 Oct 2017 18:24:47 +0000

When framing the cut rafters
When framing the cut rafters for the raised heel system how would one go about strapping the rafters to the wall in an efficient manner? It seems to me that typical truss-to-plate connectors would not be useful. The idea of raising a truss such as this is a no-brainer to become standard practice/

By: RoyC

RoyC — Tue, 19 Sep 2017 12:50:48 +0000

In reply to Alexandre D'Amours. I am not a "structural
I am not a "structural engineer", but I am an engineer that has taken some structural courses. If a single top plate "can't take ANY load", then how can a double plate be that much stronger? If I remember correctly, a beam that is twice as tall can handle 4 times the load for the same deflection, but that is assuming a solid beam. If you just stack two plates that are not bonded, it will only handle twice the load. I doubt that a nail every 16 inches between the two top plates would prevent much slipping between them, especially since the forces are with the grain. But either way, tightly connected or not, I don't see how having something that is 2 or even 4 times something that "can't take ANY load" is that much better. Either way I would still recommend aligned framing since that eliminate this issue, and a second top plate not only increases thermal bridging, it costs more.

By: Alexandre D'Amours

Alexandre D'Amours — Tue, 19 Sep 2017 11:36:13 +0000

In reply to RoyC. For what it's worth, here is
For what it's worth, here is my two cents as a structural engineer: Keep the double plate. 1.Structural diaphragms need continuous members at their edges so they can function AND they can be calculated more easily (most important for us!) 2.It would be a bad habit to start building single top plate walls all the time. What if there is a lack of coordination between the wall building and truss builder or installer? A single top plate joint can't take ANY load. That to me is a risk that far outweighs any minimal gain you would get from thermal bridging in wood. 3.Most buildings aren't inspected, so who is going to make sure those truss are really aligned with the studs? Let me know what you guys think!

By: Graham Irwin

Graham Irwin — Thu, 10 Aug 2017 04:08:58 +0000

Love the “Traffic” reference,
Love the “Traffic” reference, Allison. Some trivia: the raised heel truss is/was also known as the “Arkansas truss,” developed for the “Arkansas Project” in the 1960s. A bit about that project here: https://buildingscience.com/documents/insights/bsi-018-westford-house

By: RoyC

RoyC — Tue, 08 Aug 2017 20:59:28 +0000

In reply to LeeH. Not much ever got published.
Not much ever got published. I was involved with the design, construction, and instrumentation, but then our research funding ran out and I had to find another job. The houses are still there, but there isn't much research going on that I can see.

By: abailes

abailes — Tue, 08 Aug 2017 20:00:46 +0000

In reply to JC. JC, I agree with David. I

JC, I agree with David. I think a lot of builders just aren't aware of raised-heel trusses. (That's not true for the ones who read this blog, though!)